On Wed, Jan 10, 2018 at 3:41 PM, Roy Stogner <[email protected]> wrote:
> > On Wed, 10 Jan 2018, David Knezevic wrote: > > I'd like to use unique_ids to identify elements and nodes without worrying >> about renumbering, but before I do that I'd like to understand a bit more >> about how unique_ids are defined. >> >> In particular, what is the idea behind how we generate the unique_ids? >> > > Basically we have two constraints: > > 1. We want to never ever reuse a unique_id for two different > DofObjects of the same category (Nodes, Elems). > 2. We want to assign a unique_id to each DofObject as soon as possible. > > And that leads us to a few complications: > > 1. Our unique_id values will often be sparse: When adaptively > coarsening we delete objects, and we *don't* give their replacements > the same unique_id if/when we adaptively refine the same area again. > When building distributed meshes, we add objects on one processor > without communicating with other processors, so each processor "owns" > an interleaved subset of unique_id space, and may leave some of that > space blank. > 2. Our unique_id values are really only well-defined *when* they're > created, and that creation may depend on mesh type and partitioning. > So: > > One concrete question I have is if I create two Mesh objects by reading in >> the same mesh exodus file twice, will those two meshes have matching >> unique_ids? I guess they will simply because "add_node" and "add_elem" >> will >> be called in the same order during those two read operations. >> > > If both reads are using the same libMesh version, and either both are > to a ReplicatedMesh or both are to a DistributedMesh, then currently > the answer is yes. I don't expect that to change, though I haven't > really thought about it before. > > Please don't count on unique_id numbering remaining the same from > version to version, though! If you need to open a mesh next year with > the same unique_id numbering it has this year, save that mesh in XDR > or XDA (where we write out unique_id), not Exodus. Thanks for the explanations, very helpful! David ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
